1. Field of the Invention
The present general inventive concept relates to a hard disk drive apparatus, a method to control a flying on demand (FOD) of a hard disk drive apparatus using a thermal asperity (TA) signal, and recording media for computer program thereof, and more particularly, to a hard disk drive apparatus which can actively control a flying height (FH) of a magnetic head with respect to a disk so as to improve reliability of a read/write operation and solve general problems such as a head disk interface (HDI) caused as a uniform FOD voltage is applied to the magnetic head as in prior art, a method to control the FOD of a hard disk drive using the TA signal, and recording media for computer program thereof.
2. Description of the Related Art
Hard disk drive apparatuses (HDDs) formed of electronic parts and mechanical parts are memory devices to record and reproduce data by converting digital electric pulses to a magnetic field that is more permanent. The HDDs are widely used as auxiliary memory devices of computer systems because of fast access time to a large amount of data. With the recent increase in TPI (tracks per inch; a density in a radial direction of a disk) and BPI (bits per inch; a density in a rotational direction of a disk), the HDD has achieved a high capacity and its application field has expanded.
As the capacity of the HDD increases, a size of a read/write sensor of a magnetic head decreases and the flying height (FH) of the magnetic head gradually decreases. That is, when a high TPI and a high BPI are realized to manufacture a high capacity HDD, a width of a track decreases. When the track width decreases, the strength of a magnetic field becomes weak. Accordingly, when the FH increases, a detection of a magnetic field is difficult so that operation of the HDD cannot be smooth.
For this reason, methods of effectively reducing a spacing loss between the disk and the magnetic head, that is, reducing the FH of the magnetic head with respect to the disk, are actively being developed as a condition precedent to maximize the read/write performance of the magnetic head.
In order to actively control the FH of the magnetic head with respect to the disk, the FH of the magnetic head can be determined. To determine the FH of the magnetic head, a method of controlling a protrusion of the magnetic head using a heater sensor in a slider is used. This method is the most effective in setting the FH that is required.
In the method, a constant voltage or an FOD voltage is applied to a heater coil included in the magnetic head so that a pole tip that is an end portion of the magnetic head thermally expands during the operation of the HDD. Thus, the FH is determined using a characteristic that the FH of the magnetic head is reduced during the thermal expansion of the pole tip. A series of these techniques are referred to as flying on demand (FOD).
In conventional technology, a gradually increasing FOD voltage is applied to the magnetic head. A voltage when the pole tip of the magnetic head touches down on a flat surface of the disk is measured as the maximum FOD voltage. An appropriate FOD voltage less than the maximum FOD voltage is determined and uniformly applied to the magnetic head.
However, since the FH of the magnetic head is substantially not constant and a degree of expansion of each FOD is different, it is difficult to apply the FOD in the above method. In particular, when the FOD voltage is uniformly applied to the magnetic head, if the FH of the magnetic head is too low, the HDI that causes a physical shock is generated between the magnetic head and the disk during the operation of the HDD can be generated. Conversely, when the FH of the magnetic head is too high or the pole tip does not thermally protrude to a desired degree, it is difficult to obtain a desired clearance or gap between the magnetic head and the disk.
Also, in determining the appropriate FOD voltage, there are a variety of methods to detect how much the gap between the magnetic head and the disk can be decreased when a certain amount of a voltage is applied, or what is the maximum FOD voltage that can be applied. Accordingly, there may be a wide difference due to a rotation speed (rpm) of a spindle motor where the disk is mounted, or outside conditions. However, since its repeatability is not superior, various methods to solve the problem have been suggested. Thus, a method to solve the general problems including the HDI that is generated when a uniform FOD voltage is applied to the magnetic head as in the conventional technology, by controlling the FOD in an improved manner is needed.